The present invention concerns a method and an apparatus for optically scanning a vehicle wheel.
A typical example of a vehicle wheel to which the invention can be applied can be a motor vehicle wheel.
In one form of a method of optically scanning a vehicle wheel such as a motor vehicle wheel, a location on the wheel is sensed by means of a light beam emitted by a light source, and the light beam is reflected to a position-sensitive receiver. The spacing of the sensed location relative to a reference location is then measured from the directions of the emitted and reflected beams. That method can be carried into effect by suitable apparatus which comprises for example a shaft on which a vehicle wheel to be measured is rotatable about the axis thereof, with a light source for directing a light beam on to the location on the wheel and a position-sensitive receiver for receiving the reflected beam. A suitable actuator causes synchronous pivotal movement of the light source and the receiver about a common pivot axis, and the measurement values of the receiver are fed to an electronic evaluation system to ascertain the spacing of the location on the vehicle wheel from a reference location. Such a method and apparatus can be found in WO 98/10261. The light source can be in the form of a laser beam source and the location on the wheel, to which the light beam is directed, can be beside a balancing weight which is fixed on the inside of the vehicle wheel rim. The position of the sensed location on the wheel is ascertained by means of a suitable triangulation method.
In the apparatus structure, the light source and the receiver can be disposed on a common carrier which can be turned by hand so that the emitted light beam can be directed to the desired position at which the balancing weight is fixed on the wheel rim. The apparatus also includes a stepping motor with which, after an unbalance-measuring operation has been carried out on the vehicle wheel to be balanced, the light source alone is turned in such a way that the light beam emitted thereby is directed on to the balancing location on the wheel rim, at which the balancing operation is to be carried out, for example by fixing a balancing weight thereto.
Reference may also be made to WO 96/078830 disclosing a method and apparatus for balancing a motor vehicle wheel, in which a contour of the wheel and in particular the internal contour of the wheel rim can be ascertained by means of a scanning device. The optimum positions and sizes for balancing weights can then be ascertained from that sensed contour, in conjunction with measurement values from a device for measuring unbalance of the vehicle wheel.
An object of the present invention is to provide a method of optically scanning a vehicle wheel such as a motor vehicle wheel, with which complex wheel contour configurations such as inclined edges, rounded configurations and the like can be easily detected.
Another object of the present invention is to provide a method of optically scanning a motor vehicle wheel which involves an operating procedure of enhanced simplicity while affording reliable results.
Still another object of the present invention is to provide an apparatus for optically scanning a vehicle wheel to be balanced, which can implement accurate results while involving an uncomplicated apparatus structure.
Yet another object of the present invention is to provide an apparatus for optically scanning a vehicle wheel in which demands in terms of accuracy of the operating components of the apparatus can be readily met.
In accordance with the principles of the present invention in the method aspect the foregoing and other objects are attained by a method of optically scanning a vehicle wheel such as a motor vehicle wheel, in which a location on the wheel is sensed by means of a light beam emitted by a light source and the light is reflected to a position-sensitive receiver. The spacing of the sensed location on the wheel relative to a reference location is measured from the directions of the emitted beam and the beam reflected from the sensed location on the wheel. The emitted beam and the position-sensitive receiver are synchronously pivoted about a common axis in a measurement plane which intersects the rim surface of the vehicle wheel at an obtuse or approximately right angle, for successive measurement steps.
In the apparatus aspect the foregoing and other objects of the invention are attained by an apparatus for optically scanning a vehicle wheel to be balanced, comprising a shaft for carrying the wheel for rotation thereof about its axis, a light source for emitting a light beam on to a location on the wheel, and a position-sensitive receiver for receiving the light beam reflected from the sensed location on the wheel. A rotary drive produces synchronous pivotal movement of the light source and the receiver about a common pivot axis and an electronic evaluation system evaluates measurement values from the receiver for ascertaining the spacing of the sensed location on the vehicle wheel from a reference location. The rotary drive includes a stepping motor. A rotary angle sensor which supplies a signal proportional to the respective rotary angle position of the stepping motor is operatively connected to the evaluation system.
As will be seen in greater detail from the description hereinafter of a preferred embodiment of the invention, when the light beam emitted by the light source which more particularly can be in the form of a laser and the position-sensitive receiver which receives the beam reflected from the sensed location on the vehicle wheel are pivoted synchronously about a common axis for successive measurement steps, in a measurement plane which is substantially perpendicular through the rim surface of the vehicle wheel, in the successive measurement steps the respective spacings of the successively sensed locations on the wheel are measured in relation to a reference location which is stationary on the balancing machine on which the unbalance-measuring procedure and the balancing operation are carried out. Preferably, the respective spacings of the sensed locations on the vehicle wheel relative to the reference location are measured from the respective directions of the emitted light beam and the reflected light beam, on the basis of a one-dimensional active triangulation method. That provides for clearly determining the position of the respective sensed location on the vehicle wheel, relative to the reference location which is fixed with respect to the machine. The plurality of mutually adjoining, sensed and measured locations on the wheel can be used to very accurately ascertain the contour of the vehicle wheel and in particular the inside contour thereof.
As noted above, the sensing movement is produced by a stepping motor forming the rotary drive of the apparatus, for pivoting the light source and the receiver synchronously about the above-mentioned common pivot axis. For that purpose, the light source and the receiver can be fixed on a common carrier which is pivotable about the pivot axis.
The rotary angle sensor of the apparatus, which can be integrated into the stepping motor or which can be arranged separately, is used to detect the respective rotary angle position of the stepping motor and thus also the light source and the receiver. That rotary angle position is passed to the evaluation system together with the measurement signals from the receiver. It will be noted that the pivot axis about which the light source and the receiver are pivoted in operation of the apparatus is in a fixedly predetermined position with respect to the above-mentioned reference location which can be provided on the balancing machine, in fixed relationship with the machine.
In a preferred feature of the invention, the measurement plane within which the light source and the receiver and thus the emitted and the reflected light beam are moved extends at least substantially parallel to the axis of the wheel. When the axis of the wheel is arranged horizontally the measurement plane can extend below the axis of the wheel. It is however also possible for the measurement plane to extend inclinedly relative to the horizontal and to extend for example radially in relation to the axis of the wheel or the measurement shaft of the apparatus, on which the wheel is mounted.
In accordance with a further preferred feature of the method of the invention the emitted light beam can further be used to sense the radially extending region of the central part of the vehicle wheel within the rim thereof. In that case, it is possible to sense or ascertain angular positions of the base points of arms or spokes which extend radially from a central part of the wheel disk. Those measurement values can then be used for positioning balancing weights behind the appropriate arm or spoke, in an operating procedure as is to be found for example in U.S. Pat. No. 5,591,909 to which reference is accordingly directed.
Preferably, the pivot angle for the common pivotal movement of the light source and the receiver about the pivot axis is such that, starting from approximately the center of the wheel, the sensing emitted light beam and the reflected beam component received by the receiver from the sensed location on the wheel can be pivoted over the radially extending region of the disk portion of the wheel, the inside surface of the rim of the vehicle wheel and the tire bead.
In a further preferred feature of the method of the invention, lateral displacement, in the axial direction of the wheel, of the sensed locations of the wheel can be appropriately ascertained by means of the method.
After the procedure for measuring unbalance of the respective vehicle wheel, the emitted light beam can be directed on to the wheel at the balancing location at which unbalance compensation is to be effected, using the procedure known for example from WO 98/10261.
Further objects, features and advantages of the invention will be apparent from the description hereinafter of a preferred embodiment.